Electronically controlled low impedance phase shifting device



April 15, 1952 s. R. RICH 2,592,738

' ELECTRONICALLY CONTROLLED LOW IMPEDANCE PHASE SHIFTING DEVICE FiledSept. 19, 1945 2 SHEETS-SHEET 1 R MM l0 Ac w :5 W W i 7 7 PHASE i= s 1 RAMPLIFIER SHIFTING MEANS FIG. I |'l'|'l l I VARISTOR CONTROL VOLTAGER-oHMs MAGNIFIED 3mm STANLEY R. RICH APPLIED VOLTS D. G.

Aprll 15, 1952 s. R. RICH 2,592,738

ELECTRONICALLY CONTROLLED LOW IMPEDANCE PHASE SHIFTING DEVICE FiledSept. 19, 1945 2 SHEETS-SHEET 2 PHASE SHIFTING NETWORK FIG. 2

AMPLIFIER REGESIVER INDICATOR SWITCHING LINE grwwvbob STANLEY R. RICHPatented Apr. 15, 1952 ELECTRONIGALLY CONTROLLED LOW 1M- PEDANCE PHASESHIFTING DEVICE Stanley R. Rich, Cambridge, Mass, assignor to the UnitedStates of America as represented by the Secretary of the NavyApplication September 19, 1945, Serial No. 617,367

4 Claims.

This invention relates to means to control the phase shift in atransmission line or similar network and is particularly directed to acircuit which enables the use of varistors as low impedance variablereactance control elements.

The invention is of general application but will be described in thefollowing specification in its specific aspect which adapts it to anelectronically rotated sound echo ranging or scanning sonar system.

For the purpose of this disclosure it is necessary to understand theessentials of a scanning sonar system only to the extent that the systememploys a transducer from which an omnidirectional sound pulse isperiodically emitted, echoes from the sound pulses being picked up bythe transducer acting as a multi-element receiving microphone theelements of which are scanned at intervals less than the pulse length.Scanning is accomplished in one form of the electronic rotation systemby so biasing varistors associated in the receiving circuit of eachtransducer element as to permit the passage of current from successivetransducer elements into the rest of the receiver system.

A switching line is used in the preferred form by which a pulse starteddown the line biases each varistor in turn, thus in effect, rotating abeam of sensitivity around the transducer the frequency beingdetermined, of course, by the electrical length of the switching line.As soon as a pulse reaches the end of the line a new pulse is put intothe beginning so that the rotation is continuous at the switchingfrequency which is preferably at least 200 cycles per second.

While it is possible to scan each transducer element in turn and as aunit, a much higher output and hence better system sensitivity can beattained by combining the outputs of a plurality of transducer elements.Since the transducer is generally of essentially cylindrical shape and areturning wave front is essentially plane there is a time differencebetween the instant when a given sound wave strikes one element and theinstant when the same wave strikes successive pairs on either side ofthat element. Thus if the signals from the side pairs can be led inphase they can be made to add to the'signal from the center element sothat the. transducer, in elfect, operates as though it had a flat facecontainingall of the elements then conducting. In the electronicrotation'scanning system, a permanently connected lead line is used togive the desired results.

In order to activate a number of receiving scanning underwater 1,

circuits simultaneously it is only necessary to broaden the pulse in theswitching line so that several varistor elements have imposed on themsufficient voltage to render them conductive. If the switching pulsevaries in amplitude from beginning to end, as will be the case if thepulse is the clipped peak of a sine wave, the activated varistors willhave difierent voltages impressed so that they are in progressivelyincreasing and then progressively decreasing stages of conductivity as apulse passes down the line. Thus the signal contribution from the farside pairs is much less than the contribution from the instantaneouscenter element, the contribution increasing as the center element isapproached. The receiving pattern thus includes a properly weightedsample from the activated transducer elements shifted in phase toapproximate phase coincidence. This approximation is not as close as isdesirable, however.

It will be apparent from the geometry of the transducer-wave frontsystem that the phase shift required to bring signals in the first sidepair of elements into phase coincidence with the center element is muchless than that required to bring the signals in the second side pairintocoincidence, and that successive pairs require greater phase shift.Thus, either a compromise must be effected and slightly out of phasesignals tolerated if a constant phase shift lead line is used, or somemeans must be provided whereby the lead line characteristics are variedwith pattern rotation.

It is the primary object of the present invention to provide means tovary the phase shift characteristics of a phase shifting network inaccordance with the amplitude of an applied bias voltage.

Another object of the invention is to provide a low impedance means tovary the phase shift characteristics of a phase shifting network inaccordance with the amplitude of an applied bias voltage.

Still another object of the invention is to provide a circuit whereinlow impedance elements, such as varistors, can be utilized as reactors,so that the overall phase shift in the circuit is dependent on the biasvoltage across the varistor.

Other objects and advantages of the invention will become apparent fromthe following detailed description of one application of the invention,reference being had to the accompanying drawings in which:

Fig. 1 is a circuit diagram illustrating the principles of theinvention.

A varistor i is inserted in the circuit and a portion of the currentflowing through the load R1. is amplified in an amplifier l2. The outputof the amplifier is taken through a phase shifting means I4 back to thegenerator circuit in parallel with the generator. The phase shiftingmeans may be capacitive or inductive, so that with the amplifier outputin phase or 180 out of phase with the volt age across RL there existsthe possibility of the voltage which is placed in parallel with theoriginal generator voltage being of any desired phase and amplituderelative thereto. Thus, if the phase shifting means l4 introduces a 90phase lead and the output of amplifier I2 is 180 out of phase with itsinput, the voltage in parallel with the original generator voltage is aquadrature voltage lagging 90. The quadrature voltage may be a leadingvoltage if no phase shift is introduced by amplifier l2 and if means [4introduces a 90 lead. The parallel voltage may aid the generator voltageif the amplifier I2 and phase shift ing means both introduce 180 phaseshift, or it may buck the generator voltage if no phase shift isintroduced by the amplifier and 180 by the means It! or if the means I4is omitted and a phase inverting amplifier used. The reintroducedvoltage may have any desired phase relationship to the original voltagedependent upon the sum of the phase shifts in the amplifier I2 and phaseshifting means 45.

The contribution introduced by the parallel source across points A and Bis controlled in amplitude by any suitable means, the simplest formbeing a D. C. control voltage which biases and hence controls theconductivity of the varistor Ill. The varistor ID presents asubstantially constant resistance, both forward and backward, to a smallA. C. voltage from generator G. From an inspection of Fig. 3 it will beapparent that the generator voltage modulates the control voltage. Ifthe D. C. control voltage is replaced by an A. C. voltage it will beapparent that the voltage across C and D will be the generator voltagewhose ma nitude is varied by the control voltage which, if desired, maybe an audio frequency voltage derived from any source. The generatorvoltage may be derived from a microphone or signal transmission linewhile the control voltage may be derived from a sine wave oscillator ora switching lag line.

In Fig. 2 the invention is shown applied to an electronically rotatedscanning sonar system comprising a transducer which is diagrammaticallyillustrated as a ring of generators 2D. In effect each transducerelement acts as a small generator on reception of a signal. The rotationof the pattern or successive connection of each transducer element isaccomplished by means of a circuit including a pair of series-connectedvaristor elements associated with each transducer element which aresuccessively rendered operative to effectively couple the transducerelements to the rest of the system by a control pulse fed thereto fromswitch line 25. Accordingly the varistors are connected between therespective transducer elements and successive points on a switchingdelay line 25 which may consist of series inductances 26 and shuntcapacitors 21 into which a pulse is fed by a pulse generator 28. Theline, is, of course, terminated in its characteristic impedance 29.

A portion of the transducer voltage obtained from switch line 25 voltageis taken to an amplifier 30 which corresponds in function to amplifier12 in Fig. 1, so that its output passes through a phase shifting means32 and back through isolating resistors 34 to the several points betweenvaristors 23 and 24 in each set. By reintroducing the voltage betweenthe varistors the effect of the feed-back voltage is confined to thosevaristors circuits which are presently biased to conduction by theswitching delay line. The efiect thus rotates in accordance with thepattern rotation.

In the system as used without the present invention the value ofcapacitors 22 is chosen to efiect the best possible compromise toapproximate a fiat-face transducer on reception. The phase shiftintroduced by capacitor 22 has been made constant at about one radianper section. This value is slightly low for the outside sections tocontribute most efiiciently and slightly high for the most efficientcontribution from the first and second side pairs of transducerelements. a

In the operation of the present invention as applied to the specificcase shown in Fig. 2, generator 40 produces a voltage at point Y whichis advanced in phase by the line section XY so that at point X the phaseof the voltage due to generator 40 is normally 1 radian ahead of thephase at point Y. When the varistor at point X is so biased that itsresistance to the fiow of signal currents is small, signal from point Xis conducted to amplifier 30 through the associated varistors 2324 andswitch delay line 25. This signal is amplified and its phase shifted anappropriate angle. This amplified and phase shifted signal is then fedback into the circuit between varistors 23 and 26 so that a currentflows into X due to the reintroduced voltage. This produces a newvoltage at X, which, combined vectorially with the original voltage atthis point from generator 40, results in a new final voltage. The phasedifference between the new resultant voltage and the original voltage atpoint Y is now smaller than the phase difierence originally exist ingbetween points X and Y. The new phase difference is now more nearlyproportional to the actual delay in the arrival of signal from aso-urcein the medium indicated by the distance Ll.

Since the switching pulse is shaped to provide a lower bias voltage forsuccessive side pairs of circuits associated with transducer elementsflanking the instantaneous center, the varistors in these circuits areless conductive than the center varistors adjacent point X. Thus it canbe seen that the voltage contributed to point X from point Z is lessthan that from point Y, and since this voltage is made up of what may betermed a normal component added vectorially to a phase shifted componentwhich is the same in all of the varistor circuits the phase of thevoltage will be more greatly changed. The greater change is due to thefact that the phase shifted component plays a larger part in determiningthe final phase of the voltage. The result is to bring the signalvoltage from Z into more accurate phase coincidence with the signalvoltage at X and to reduce the phase relation to a value very close tothat of the actual delay in arrival time between the transducer elementsat X and Z. The same effect is present in all the activated circuits;that is, the phase lead is changed from the compromised value to onemore closely approaching the optimum.

Varistors are useful as control elements in the low impedance range froma few ohms up to about 500 ohms. Diodes may be employed successfully inthe range from 500 to 5000 ohms; and triodes, pentodes, etc. forcircuits above 5000 ohms.

What I claim is:

1. In a sonar scanner an arcuate array of transducer elements eachcoupled to a transducer output, a pulsed switching delay lineterminating in a characteristic impedance and having a number of equalincremental line impedances corresponding to the number of saidtransducer elements, circuit means connecting the transducer elementoutputs to successive ones of said incremental line impedances,respectively, a varistor in each said circuit means, whereby a pulsedvoltage progressing along said switch line causes voltages fromsuccessive transducer elements to be conducted through said varistors,respectively, an amplifier connected to said transducers through saidvaristors whereby the respective transducer outputs voltage is coupledto said amplifier upon conduction of the associated varistor, a phaseshifting network in the output circuit of the amplifier, and meansconnecting the output circuit of said phase shifting network to saidtransducer output, whereby the output thereof is the vectorial sum ofthe shifted and unshifted voltage components.

2. A transducer scanning device for converting the reception pattern ofan arcuate array of transducer elements from an arcuate to plane frontcomprising a plurality of transducer elements arranged generally alongan arcuate line, a separate transmission path connecting each transducerelement to a common circuit through a respective switch device having anormally high impedance condition and which is switchable to a lowimpedance condition, a delay line, a source of voltage pulses connectedto said-delay line for causing pulses to be sent down said line, meansconnecting said respective switch devices to different points on saidline for causing said switch device to assume a low impedance conditionin response to a pulse on said delay line to progressively couple saidtransducer to said common circuit, a phase shifting circuit coupledbetween said common circuit and the side of said switch devices remotefrom said common circuit to feed back to said common circuit a phaseshifted component of the signal therein only when the associated switchdevice is in the low impedance condition.

3. The combination of claim 2 characterized further by capacitor meanscoupled between said transmission paths for coupling a phase advancedcomponent from one transducer transmission path to the adjacenttransmission path, the said source of voltage pulses providing pulseswhich have a gradually diminishing amplitude at the leading and trailingedges thereof, the duration of said pulses being sumciently long that atleast three adjacent switch devices are simultaneously in a lowimpedance condition and hence operative to simultaneously couple aplurality of transducer elements to said common circuit, the impedanceof said switch devices, and hence their coupling eihciencies beingvariable with the instantaneous amplitude of the pulses fed thereto fromsaid delay line.

4. The combination of claim 2 characterized further by said switchdevices each including two varistor elements in series circuit relationwhich are conductive in only one and the same direction, the connectionor the switch device to the output of the said phase shifting circuitbeing made at a point between said varistor elements.

STANLEY R. RICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,971,688 Lange Aug. 28, 19341,995,708 Fischer Mar. 26, 1935 2,144,865 Wilson Jan. 24, 1939 2,188,671Wilson Jan. 30, 1940 2,286,450 White et a1 June 16, 1942

